Method and means for starting synchronous motors



Jan. 17, `1939. R. c. SCOTT 2,144,549

METHOD AND MEANS FOR STARTING S-YNCHRONOUS MOTORS Filed July '5, '19,52

MAIN LINE DIRECT CURRENT A C 7|/ 75 ExlTATN @nl /7 n n n E] FIELD RnEosTAT viii/ya Patented Jan. 17, 1939 I UNITED STATES PATENT OFFICE Mn'rnon AND MEANS 'Foa STARTING sYNonaoNoUs morons Robert C. Scott, Cambridge, Mass., assigner to General Electric Company, a corporation of New York Application July 5, 1932, Serial No. 620,858

14 Claims. (Cl. 172-289) This invention relates to new and improved ance. The starting maybe accomplished by rst methods and means for starting synchronous applying a reduced voltage to the armature Windmotors. ing and when the motor has accelerated to ap- One of the objects of my invention is to proproximately half its rated speed to then apply 5 vide a method and means'whereby the angular full-line voltage to the armature windings. Or, s position of the field structure relative to the movfull-line voltage may be initially applied to the ing wave of ux in the air gap at the instant at armature winding without first applying a reduced which direct-current excitation is applied to the voltage. y iield circuit, maybe adjusted so as to insure most In either case, the motor is allowed to attain l favorable conditions for pulling into step. its maximum induction-motor speed before dilo Another object is to provide a method and rect-current excitationis applied to the eld windmeans whereby the application of direct-curing and the starting resistance is disconnected. rent excitation to the iield circuit may be so timed After a synchronous motor has attained its as to occurat that point of the Wave of induced maximum induction motor speed, ii the direct- M ileld current at which most favorable conditions current excitation is applied to the ileld circuit l for pulling into step are obtained. at random the motor may pull into step Without Another object is to provide a method and slipping more than one pole and run as a syn-i ineans whereby a synchronous motor may be chronous motor. it may continue to operate pulled into stepwith a greater shaft load than an induction motor hut with severe current and 2o would he otherwise obtainable. torque pulsations, or it may slip several poles and g@ Another object is to provide a method and then pull into step. means of limiting the armature current to a mink Three methods of controlling the application ci mum value upon closure oi the ilele switch. direct-current excitation to the eld ciroirlt ci Another object is to provide a method and synchronous motors are commonly used, means ci? relieving the revolving field structure In the first method the field switch is operan and shaft or excessive mechanical strains and. by hand or by electrical means controlled stresses during the starting period. hand-operated switch and the instant that Other objects of my invention 'will appear more tation Voltage is applied is determined fully hereinatter, the novel combination ci eleing the motor speed and the magnitude 3o ments lacing pointed out in the appended claims. armature current as indicated hy suitable insha 'My invention will he well understood loy referments. ence to the following description oi the specific in the second method the i'ield switch is op su embodiment thereof shown by way oi example in ated automatically through the action o" relay the accompanying drawing, wherein which is adjusted to operate at a predeter 55 meure l is a view chiefly in the form of a dlatime after the initiation of the startine gram ci a system illustrative oi my invention 1e' showing hy way ot example, and not 'oy Way or limitation, its application to a synchronous motor of the type which is started ley applying full volt- Ori uw 4o age directly to the armature; L3@

Fig. il is an enlarged detail; and

3 a showing a typical example of thel variation with time ci angular elisplaceseparately or together: ment een the Wave oi air-gap ilus and the (a) When the motor a I i5 field structure and oi the induced iielol current, Speed or slip, or when the frequency i 6.3

when the motor has approached or attained a duced Jfield. current decreased to a p speed suitable for applying voltage to the field mined value.

circuit. it also shows the effects ci closing the (h) When the value ci the in field switch at various instants during the cycle circuit, or of the voltages across a reactor of variation oi angle between the wave oi airnectedv in the field circuit, attains or i gap flux and the eld structure and ci variation a predetermined value.

o the induced field current. (c) When the cycle of induced ielcl current Synchronous motors, regardless of type, are of a certain direction of pulsatiose. usually started as induction motors with the field I rxd thatwith any oi these methods oi 'coofcircuit short circuited through a starting resisttrolling the closure of the held switch, an increase 5g cante effected in the amount of shaft 'load which can becarried and pulled into step and' a. reductioned' commonly used methods of controlling the application of direct-current excitation to the field circuit do not provide any means of relating the instant of operation of the field switch to the angle between the wave of air-gap flux and the ileld structure, or in relation to any particular instant or point onA the wave of induced field current. Also that the tlurd mentioned commonly used method merelycontrols the operation of the field switch so that closure shall occur somewhere in a positive cycle of induced iield current y or somewhere in a negative cycle of induced ileldcurrent. i

`Due to the unsatisfactory and'highly irregular results obtained with starting methods as hitherto employed, it was to be deduced that there was some particular instant relative to the electrical condition ofthe system in which starting couldbe effected with optimum results, but the matter had not hitherto been fully understood. A mathematical solution has not been possible `since the differential equation of motion of a synchronous motor could be solved' only for limited values and with an expenditure of great effort so that it was impossible to arrive at results by calculation from which conclusions could be deduced. By mechanical integrating methods I have been able to investigate the subject and I have determined the importance of the angle between the moving Wave of air-gap'flux and the eld structure, and have discovered, moreover, that by applying' direct-current excitation to the eld circuit of the motor with proper observance of this factor, unexpectedly high increases in eiliciency as regards the shaft load carried as well as other improvements in operation during the starting period may be obtained.

The subject may be more fully understood by reference to Fig. 3 in which I have shown by Yway of example a typical 4graph showing for one particular motor the relative relations of the current induced in the eld circuit, the angular displacement between the ux in the airgap and the ileld structure and the maximum value -of Y' shaft load which can be pulled into step when direct current excitation is applied at various instants. This graph, of course, represents om. particular-but typical motor and represents conditions at the time when the motor has obtained its maximum speed as an induction motor. More specifically, the curve a shows the variation with time of the current induced in the field circuit. The curve b shows the variation with time of the angular displacement between the ilux in the air gap and the held structure; The curve c, d, e, f, 0. h showsvthe variation with time of the maximum value of shaft load which can be pulled into step when direct current excitation is applied at various instants. Since the curve c, d, e, f, 9, 'h

y represents maximum values. of load, of coarse lesser values can be pulled into step, and Wemay therefore say that points that lie within the area bounded by the curve and horizontal axis are de- Vfined by values of shaft load and switching angle for which a motor will pull' into step without swinging beyond the first region of motor action. Points lying within the shaded area bounded by d, Ve. j denne values of shaft load and switching angle for which a motor will pull into step in the next region of motor action after ilrst passing through a complete region of generator action. Points within these two zones are the only ones for which a motor will pull into step with the steady-state operating angle not more than 360 electrical degrees from the initial switching' angle. Points lying within the shaded area above line d, f and g deilne values of shaft load and switching angle for which a motor will eventually will never pull into step but will continue to run as an induction motor with severe current, torque and slip pulsations. It should be understood that the statements just 4made concerning these zones are statements of fact on the basis of the mathematical investigations referred to as well as experimental concurrence as illustrated by the particular example shown.

Referring again .to the figure, in the zone bounded betweenthe vertical Alines k and l the direction of eld current pulsation is opposite to the direction of excitation current. Also in the zone bounded by the vertical lines l andm the direction ofield current pulsation is the same as the direction of excitation current. Now for the particular example represented by the typical curve shown it will be apparent from the ligure that the maximum load which can be pulled into step will be obtained if direct current excitation is applied when the angular position of the eld structure relative to the movin'g wave of flux in the air gap is approximately minus 30 electrical degrees, say at thev point p. It will be observed further that if the excitation is applied merely when the cycle of induced eld current is at a certain direction of pulsation, for instance,l in the half cycle between the lines k and l in Fig. 3, it would be possible to switch the ield at an instant such that the motor would swing through a number of cycles before pulling into step, even if the shaft load were less than the maximum load which could be pulled into step if excitation were applied at the desirable angle; for instance, in the example shown, at a time value slightly to the left of l'ine l.

It should be borne in mind tha-t the curves of Fig. 3 are exemplary merely and will diil'er cussed is shown diagrammatically in Fig. 1 whereby way of example merely I haveshown a motor of the type which is started by applyingv full voltage directly to the armature. Referring to -this figure of the drawing, I there show the mo' tor having armature supplied with alternating current through4 circuit breaker 1. The iield 9, when the motor is in operation, is supplied with direct current through the main eld switch Il. During starting it will be understood thatv the ileld lswitch Il is open and the ileld Winding iis short-circuited through wire I3, starting resistance l5, field discharge switch |1 and wire The supply of current to the armature energizes, through transformer 2|, the coil of relay 23. This relay is provided with means for delaying its action until the motor obtains substantially its maximum speed as an induction motor, this herein being diagrammatically indicated by the showing of the dashpot 25. When the relay closes the upper bridge 21 thereof` this closes the circuit of the polarized relay device 29 seen at the lower right hand portion of the figure which is associated with the circuit of iield 9 in a suitable manner, herein by means of a suitable shunt 3|. Starting at this shunt, the circuit of the relay 29 is through wires 33, and 3d, bridge 35 hereinafter to be referred to, wire 3V, the bridge 21 of the relay 23, wire 39 to the relay 29, and from relay 29 through wire 4| back to the shunt 9i.

The illustrative con truction of relay 29 here disclosed by way of example comprises two sets of coils operating respectively the armatures 43 and 45, the arrangement being such that when a current or given polarity is flowing through the relay, the armatures tend to move in the same direction, that is, to the right or left as the case may be. The coil springs 41 and 49 tend respectively to hold armature 43 to the right in the dotted line position shown and armature 45 to the left in the dotted line position shown. When in the full line position shown in the iigure, the'armature 43 cooperating with an adjustable contact 5| closes the circuit between the terminal posts 53 and 55.

Armature 45, which may end with a roll as shown, serves as a cam operating, when swung to the left from the full line position of the figure, to lift against the force oi spring 51 the swinging arm A59 provided at its end with a pawl 6| which, when the arm is lifted, is in the path of armature 43 as it moves to the left from the dotted line to the full line position shown, the pawl being yieldably mounted to permit the armature to swing freely in the opposite direction. Suitable means may be provided for preventing armature 45 from being swung to the left too promptly by its spring 49, and I have herein shown an arm 63 extending therefrom adjustably connected (see Fig. 2) to a pawl-carrying lever 65 which cooperates with a ratchet be provided at its wheel 51, the turning of which is braked by the vane 69. Thus armature 45 can move freely to the right, the pawl slipping over its ratchet, but on its return movement the ratchet is engaged, the vane must be turned against the resistance of the air and too rapid movement of the armature to the left is thus prevented. Prior to energization the armatures are, of course, in the dotted line position shown.

Assuming now that when the mechanism is energized the polarity of the current is such as to tend to pull both armatures toward the left, the armature 45 supports arm 59 in raised position and prevents movement of the armature 39 to the left to close its contact. On the next reversal of direction of the induced field current both armatures will be pulled towardv the right. Armature 45 takes the full line position shown,

permitting the arrn 59 to drop. 0n the following reversal of vpolarity both armatures will oscillate to the left and armature 43 will return to the full line position to close the circuit before armature 45, the movement of which vthe half cycle of desired is braked by the vane 69, will interpose pawl 6I in its path.

This construction is an example of a mechanism which when energized will not act until polarity which begins after the time of energization. The importance of this is more accurately expressed by saying that it will not act during a half cycle of desired polarity which was commenced prior to its time of energization.

When relay 29 is operated in the manner described, current flows through it from the transformer .1| to the coil of relay 13, the circuit being as follows: wire to relay 29, thence by Wire 11 to the coil of the relay and back through wire 19. The relay 13 is small and fast in its operation and is preferably provided with a bridge 16 which is closed on the slightest impulse of the operating coil to provide a holding circuit to maintain the relay energized after the armature of the polarized relay oscillates to its original position. This holding circuit leads from wire l5 through branch 8i, bridge 83, wire 85, bridge 16 just referred to, through the coil of relay 13 and back through wire 19. Actuaton of this relay 13 also closes lower bridge gli, energizing the coil of relay 89, the circuit thereof being from wire 15, wire 9|, the coil of the relay, wire 93, bridge 81, wire 19. The relay 89 is adjustably retarded in any suitable manner, as diagrammatically indicated herein by the showing of the dashpot 95. It will be understood that since the polarized relay acts substantially at the beginning of a half cycle, this adjustment permits the bridge 9i! operated by the relay to be closed at the'desired time during that half cycle to insure supply of direct current to the motor field at the desired angle. l

Closing the bridge 91 energizes the operating coil 99 oi the main field switch, the circuit leading from the positive line through that coil to wire |01, bridge 91 and wire |93 to the negative side. The field switch moving to the left under the influence of this coil first closes bridge |05 which forms a holding circuit for the coil 99 leading from the positive side of the line through the coil, through wire |01, bridge |95, wire |99, the lower bridge itl of relay 'l and wire ||3 to the negative side of the line.

Closing of the main field switch il applies direct current to the field and at substantially the same time, or slightly subsequently thereto, the arm H5 is rocked clockwise, opening field discharge switch il and breaking the circuit which includes field 9 and. the starting resistance l5. This main field switch mechanism also opens bridge 35, thus deenergizing the polarized relay mechanism 29. The relay 89, when completely closed also opens bridge 83 shown immediately above the same, thus deenergizing the relay 13, the deenergizing of which in turn breaks the circuit of relay 89 at bridge 8l.

The time. required for field switch to close after the coil 99 is energized depends on the design of the switch but may be considered to be constant. Also the time lag, if any, of the polarized relay :mechanism 29 may be considered to be conetant. So that for a given shaft load it is oniy necessary to introduce the proper time lag between the closing of the contacts of relay 29 at 43, 55|, and the closing or the field switch contacts it in order for the iield switch always to close at a desired angle. Such time lag may be effected by adjustment of the response of the relay 89, Given an installation and mechanism such as shown or its equivalent, the adjustment 4- relative magnitudes -and of the induced eld for the given motor may be readily effected after installation of the' of both the armature field currents during the starting period.

While I have shown one style of polarized relay and one style of -time delay relay and a certain conventional circuit, it is apparent that this invention covers broadly anymethod or means controlling any part or all of the pulling into step phenomena of a synchronous motoror synchronousmachineoi'v any type such as rotary and ' converters, synchronous condensers and alternators, through an automatic means responsive to the electrical condition of the eld circuit, for supplying direct-current excitation to the field circuit when the angular displacement between the wave of air-gap flux and the field structure current, has substantially a predetermined value.

While Vthis invention has been described as applied to its use with a synchronous motor of the type which is started by applying full voltage directly to the armature, yet the method vand means for pulling into step may be applied to synchronous motors of the type which is started by first applying reduced voltage to the amature.

I am aware that the invention may be er'nbodied in other speciiic forms without departing from the spirit or essential attributes thereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive; reference being' had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

' I claim:

1. In a system ofthe class described, the combination with a synchronous motor having` a ileld winding, means for running said motor as an induction motor, a relay mechanism to which the induced eld current is applied when the motor 'attains substantially its maximum speed as an induction motor, and comprising a relay arranged to operate on a pulse wholly succeeding the pulse during which the current is applied, and means controlled by the relay to apply ex'- citation current to the ileld comprising an adjustable timing mechanism.

2. In a system of .the class described, the combination with a synchronous motor having a iield winding, means for running said motor as an induction motor, arelay responsive to a uni.-

' directional current only energized by the inducedv iield current when the motor attains substantially its maximum speed as an induction motor, means to prevent effective operation of said relay during a pulse initiated prior to the energizemeans responsive to the operation of said relay to apply excitation .current to the field at a predetermined `time thereafter.

3. In a system of the class described, the combination with a synchronous motor having a field winding, means for running said motor as an induction motor, a relay responsive to a unidirectional current only energized by the induced iield current when the motor attains substantially its maximum speed as an induction motor, a detent normally opposing closing movement of said relay, means responsive to a determined polarity of the current to retract the detent, ,and means -responsive apply excitation current to the field at a predetermined time'thereafter. 4. In a starting system iior synchronous motors, in combination, a motor provided with ileld equipment by observing the tothe closing of the relay to' and armature windings, means for controllingtheenergization of the armature winding, a switch for controlling the energlzaticn of the ileld winding, a time-delay relay responsive to the voltage applied to the armature winding and ,disposed to prevent the energization of means for applying voltage .'to the ield windingifor a predetermined time interval after `the application of voltage to'the armature winding, an instantaneous relay disposed to be energized by the voltage induced in the field winding subsequent to the operation of the time-delay relay, said instantaneous relay being operatively responsive tocurrent of asingle polarity only, means responsive to the action of current of opposite polarity initiating the operation of said rst means, and a second time-delay relay disposed to be energized subsequent to theenergization 4oi the second instantaneous relay for applying excitation yoltage to the iield winding to eect a maximum cumulative relation between the torqueresulting from the application ci? voltage to the armature winding and thetorque resulting from the application of voltage to the iield winding.

5. In combination, an alternating current cirwinding connected tov said circuit and a field saidbmachine, and means responsive to said timing means completing its timing operation for connecting' saidrsource of excitation to said iield t 6. In combination, an alternating current cir, cuit, a synchronous machine having an armature Winding connected to said circuit and a iield cuit, a synchronous machine havingan armature winding, a source oi excitation forsaid iield winding, and means for connecting said source of excitation to said field winding at a predetermined optimumA angular relation between said iieldl winding and the air gap ilux of said ma-` chine including timing means having a deilnite time of operation, means responsive to a preded termined electrical condition of one of the windings of said machine .for initiating the timing operation of said timing means at a denite angular relation between said ield winding and the air gap iiux of said machine, and means responsive tosaid timing means completing its timing operation for connecting said source -of excitation to said ield winding.

7. In combination, an alternating current circuit, a synchronous machine having an armature winding connected to said circuit and a field winding, a source of excitation for said eld winding, and means for connecting said source of excitation to said eldwinding at a predetermined optimum'iangular relation between said eld winding and the air gap ux of said machine including timing means having an adjust` able definite time voi! operation, mea' s respon` siveito a predetermined current'condition in'one of the windings v,of said machine when Asaid machine is operating at substantially synchronous speed as an induction Imachine for initiating the timing operationl of said timing means at a definite angular relation between said field winding and the air gap flux of said machine, and means responsive to said timing means completing its timing operation for v-nnecting said source of excitation to said nein winding.

8. In combination, an alternating current circuit, a synchronous machine having an armature winding connected to said circuit and a fleld winding, a source of excitation for said field winding, switching means for connecting said source of excitation to said field winding and having a definite operating time, and means for effecting the operation of said switching means so that said sourceof excitation is connected to said field Winding at a predetermined optimum angular relation between the field winding and the air gap flux of said machine including timing means having an adjustable time of operation, means responsive to a predetermined electrical condition of said field winding for initiating the timing operation of said timing means at a definite angular relation between said field winding and the air gap flux, and means responsive to said vtiming means completing its timing operation for initiating the operation of said switching means.

9. In combination, an alternating current circuit, a synchronous machine having an armature winding connected to said circuit and a field winding, a source of excitation for said field wind-s ing, switching means for connecting said source of excitation to said field winding and having a definite operating time, and means for effecting the operation of said switching means s'o that said source of excitation is connected to said field winding at a predetermined optimum angular relation between the field winding and the air gap flux of said machine including timing means having an adjustable time of operation, means responsive to the induced current in said field winding for initiating the operation of said timing means at a definite point in the slip cycle, and means responsive to said timing means completing its timing operation for initiating the operation of said switching means.

10. In combination, an alternating current cir cuit. a synchronous machine having an armature winding connected to said circuit and a field winding, a source of excitation for said iield winding, switching means for connecting said source of excitation to said field winding and having a definite operating time, and means for effecting the operation of said switching means so that said source oi excitation is connected to said field winding at a predetermined optimum angular relation between the field winding and the air gap ux of said machine including timing -means having ran adjustable time of operation,

polarity responsive means responsive to the induced current in said field Winding for initiating the operation of said means at a definite point in a definite hali cycle of slip oi saiel machine, and means responsive to said timing means f completing its timing operation for initiating the operation of said switching means.

il. In combination, an alternating current circuit, a synchronous machine having an armature winding connected to said circuit and, a held winding, source of excitation for said field win@ ing, switciiing means for connecting said source of excitation to said field winding and having a definite operating time, and means for eecting the operation of said switching means so that said source of excitation is connected to said field winding at a predetermined optimum point ofthe wave of induced field current when said motor is operating at a predetermined subsynchronous speed including timing vmeans having an operating time equal to the difference between the time it takes the induced field current to change from a definite point on said wave to said `optimum point at said predetermined subsynchronous speed and theoperating time of said switching means, and means responsive to the electrical condition of one of the windings of said machine for initiating the operation of said timing means at said definite point of said wave of induced field current at said'pred'etermined subsynchronous speed.

12. In combination, an alternating current circuit, a synchronous kmachine having an armature winding connected to said circuit and a field winding, a source of excitation for said held wind ing, switching means for connecting said source of excitation to said field winding and having a definite operating time, and means for effecting the operation of said switching means so that said source of excitation is connected to said elcl 'winding at a predetermined optimum point of the wave of .induced field current when said motor is operating at a predetermined subsynchronous speed including timing means having an operating time equal to the difference between the time it takes the induced held current to change from a definite point on said wave to said optimum point at said predetermined suhsynchronous speed and the operating time of said switching means, and means responsive to the electrical condition of said field winding for initiating the operation of said timing means at said definite point of said wave of induced eld current at said predetermined subsynchronous speed. f

13. In combination, an alternating current circuit, a synchronous machine having an armature Winding and a field winding, switching means for connecting said armature winding to said circuit, a source of excitation for said field winding, and means for connecting said source to said field winding at a predetermined optimum pointon the wave of induced iield current when said machine is operating subsynchronously as an induction machine including timing meansl having a definite time of operation, means re sponsive to an electrical condition of said machine for initiating the timing operation of said timing means at a definite point on the wave .of induced field current, means responsive to said timing means completing itstiming operation for connecting said source of excitationto said field winding, and other timing means controlled by said switching means for rendering said electrical condition responsive means operative to control said first mentioned timing means after said armature Winding has been connected to said circuit for a predetermined time.

14. In combination, an alternating current circuit, a synchronous machine having an armature winding and a field winding, switching means for connecting said armature winding to said circuit, a source of excitation for said field winding, and means for connecting said source tov said field winding at a predetermined optimum point on the wave of induced field current when said machine is operating subsynchronously as an induction machine including timing means having a definite time of operation, means responsive to 6 Y I `2,144,54o

point on .the wave of induced iield current, means A snonsive to said timing means completing its timcontrolled by said switching means for renderingv im;r operation for connectingv said source oi said induced field currentI responsive means opexcltation to said field winding. n erative to control said timing means after said 5 amature winding has been connected to said ROBERT C.-BCQT1. l

circuit for a predetermined time.. and means re- 

